This proposal is aimed at using iPSC technology to create model systems in which to study the pathophysiological consequences of addiction-associated gene variants. The cell lines, differentiation methods, and characterization methods will aid in development of screening assays for compounds that may be useful for the treatment of addiction. The mesolimbic dopamine system is known to be involved in drug abuse. It has multiple roles in giving incentive salience to stimuli in the environment, in promoting performance of goal- directed behavior and in mediating the reactivity of the organism to the environment. Variations in several gene families have been found to be associated with addiction; the nicotinic subunit receptor genes in the CHRNA3-CHRNB4-CHRNA5 region as well as CHRNA4 and CHRNA6, the A118G polymorphism of the opioid receptor OPRM1, and mutations in the TTC12-ANKK1- DRD2, among others. Some of these polymorphisms are in genes that are expressed in DA neurons and therefore have the potential to directly affect the function of these neurons. To address the role of these genetic variations, we propose to establish DA neurons from iPSC lines carrying common polymorphisms in catechol-O-methyltransferase (COMT), the a4 nicotinic receptor (CHRNA4) and the TTC12-ANKK1-DRD2 region that includes the D2 dopamine receptor (DRD2). These DA neurons will have the potential to shed light on the functional significance of these variants in addiction. Specifically we proposed to optimize protocols for generating functional central dopaminergic neurons from multiple human induced pluripotent stem cell (iPSC) lines (Specific Aim 1); characterize the phenotypes of the DA cells obtained in specific aim 1 with electrophysiological and morphological methods (Specific Aim 2); generate DA neurons form iPSC derived from individuals with mutations relevant to nicotine abuse and to investigate the effects of specific mutation on their electrophysiological properties.